Transducer suspension



Jan. 30, 1962 E. M. WEISS TRANSDUCER SUSPENSION 2 Sheets-Sheet 1 FiledJuly 11, 1960 Arrolezxgys.

Jan. 30, 1962 E. M. wr-zlss TRANSDUCER SUSPENSION 2 Sheets-Sheet 2.

Filed July 11, 1960 INVENTIORJ Ill ATTORNEYS.

3,019,306 TRANEEDUCER SEUEENSHON Erwin M. Weiss, hicago, lllh, assignorto Beltane Hearing Aid Qompany, a corporation of lllinois Filed .lulyE1, 1969, 42,152 ltl fist-Ems. (till. 179--i46) This invention relatesgenerally to transducer suspension means, and more particularly to a newand improved means for mounting a transducer in a case, as for example,the case of a hearing aid of the type adapted to be worn on the head orbody of a hard-of-hearing person.

Prior art means for mounting transducers in compact electricalapparatus, such as hearing aids, have certain characteristics in common.For example, those skilled in the hearing aid art know that some type ofvisco-elastic substance generally is used to suspend a microphone and areceiver within a hearing aid case. In some instances, the substance maytake the form of a porous blown natural or synthetic rubber, and inother cases, this substance may take the form of a sheath of solidrubber.

A transducer mounting of the first type comprising suspension members ofblown rubber cemented between the hearing aid case and the transducer isshown in Paent No. 2,894,076 granted to Sam Posen on March 17, 1959. Inthe second type of transducer mounting referred to above, the transduceris encased within a thin rubber enclosure and the entire assembly ispositioned in the hearing aid case.

In order to provide proper isolation of a transducer Within a rigidcase, it is necessary that the visco'elastic substance interposedbetween the transducer and the case be very compliant. As a result,blown rubber mountings frequently are used but it is diihcult tomaintain uniformity therein due to the wide variations in the compliancecharacteristic which exists from batch to batch, and even from portionto portion within the same batch, in a blown rubber mounting.

Further, it usually is necessary to cement the blown rubber mounting toboth the case and the transducer. Those skilled in the art appreciatethat difiiculties often arise from such an arrangement due to thetendency of the cement to rise by capillary action into the porousrubber material. As a consequence, the porous rubber material isstiilened considerably after the cement is dried and the compliantproperty which is desired is substantially lost. An additional'dilliculty arises where small sections of porous rubber are used in theform of buttons or washers. It is necessary to hold such parts to closedimensional tolerances due to the small size of the cavities in whichthe transducers are mounted, and it often is very difficult or evenimpossible to hold a piece of material with such poor dimensionalstability as blown rubber to the desired close tolerances.

In those instances where a sheath of solid rubber is used to support atransducer within a case, other difficulties are encountered. Forexample, the compliance provided by such a solid rubber sheath is notvery great, and consequently the transducer is not adequately isolatedfrom case vibrations. Those skilled in the art appreciate that the poorisolation properties of a hard thin rubber sheath frequentlynecessitates considerable reduction in the average gain of the hearingaid.

It is further known that transducer mountings which utilize resilientrubber bumpers or washers form isolators which are compliant inhorizontal as well as vertical modes. Thus, when a soft rubber bumper isused to support a microphone, the microphone tends to float sideways andas a consequence, the microphone may hit the case when the wearer moveshis head sharply.

Accordingly, it is a general object of this invention to overcome theabove-stated difi'iculties which characterize the transducer mountingmeans of the prior art.

More particularly, it is an object of this invention to provide a newand improved transducer mounting means which is characterized by itsuniform and lasting compliance properties, by its efficiency ofisolation in a desired mode, and by its relatively simple and low costconstruction.

In accordance with one specific illustrative embodiment of thisinvention, the novel transducer mounting means takes the form of a flatmetallic spring which is shaped to provide considerable effective lengthin a small area. Advantageously, the fiat metallic spring may comprise aplurality of beams connected in series with the opposed ends of thespring being fastened to the case and with the center beams beingadapted to receive and support the transducer.

As explained in greater detail hereinbelow, the fundamental trequency ofoscillation of the metallic spring isolator in combination with thetransducer advantageously is made well below the lowest frequency to beamplified by the hearing aid. In addition, it is known that atransducer, such as a microphone, is much less sensitive to vibration ina horizontal plane than in a plane perpendicular to the diaphragm. Themetallic spring isolator comprising the invention is made to be verystiff in a horizontal plane, but very compliant in the vertical plane sothat a microphone may be supported in a small cavity with less concernabout the problem of rapid head motion.

In accordance with a further feature of the invention, the metallicspring isolator is provided with particular damping means to preventexcitation into resonance at higher frequencies. Such damping meansadvantageously may comprise a visco-elastic substance sandwiched betweenthe spring isolator and a thin sheet of metallic foil, or alternatively,it may take the form of a dynamic vibration absorber in which additionalspring and mass means are secured to the spring isolator.

It is a still further feature of this invention to utilize the dampedspring isolator as a two terminal electrical conductor to reduce leadbreakage in the transducer. Thus, one electrical lead of the transduceris connected to the metallic spring of the isolator and the otherelectrical lead is connected to the metallic toll of the isolator. Sincethe connections are made at the geometric center of the suspensionsystem when there is no relative movement between the transducer and theisolator, the leads are not caused to vibrate and breakage of the leadsis substantially reduced.

The novel features which are characteristic of the invention are setforth with particularity in the appended claims. The invention itself,however, both as to its organization and operation, together withfurther objects and advantages thereof, will best be understood byreference to the following description taken in conjunction with theaccompanying drawings in which:

FIGURE 1 is a side elevational view of a behind-theear type of hearingaid, partly broken away and partly in section, embodying the presentinvention;

FIGURE 2 is a cross-sectional view of a microphone supported by ametallic isolator taken substantially as shown along line 2-2 of FIGURE1;

FIGURE 3 is a cross-sectional view of a receiver supported by a metallicisolator taken substantially as shown along 33 of FIGURE 1;

FIGURE 4 is a plan view of one specific illustrative embodiment ofmetallic isolator in accordance with the invention;

FIGURE 5 is an elevational view of a transducer sup ported by a dampingmetallic spring isolator;

FEGURE 6 is a schematic diagram of the electrical equivalent circuit ofa damping dynamic vibration absorber in accordance with the invention;

FIGURES 7 and 8 are elevational and plan views respectively of onespecific illustrative embodiment of a damping dynamic vibration absorbertype of transducer isolator in accordance with the invention; and

FIGURES 9 and 10 are plan and elevational views respectively of a dampedtransducer isolator embodiment in which the metallic elements of theisolator also serve as a two terminal electrical conductor to reducetransducer lead breakage.

Referring now to the drawing, and more particularly to FIGURE 1 thereof,there is shown one specific illustrative embodiment of hearing aid inwhich a portion of the cover has been removed from the case to betterillustrate the internal construction of the hearing aid. The presentinvention is shown in this application as used with a hearing aid forillustrative purposes only, and it will be obvious to those skilled inthe art that the invention finds equally advantageous use in other typesof compact, electrical devices which utilize a transducer, such as amicrophone, a receiver, and the like.

FIGURE 1 shows a hearing aid of the type sometimes referred to as abehind-the-ear model, which is adapted to be supported upon the ear withthe main case of the hearing aid resting on the back portion of the ear.As shown, the hearing aid v1t comprises a case 12 which advantageouslyis of channel shape to receive the hearing aid component therein. An airtube 14 extends from the upper end of case 12 and serves to convey soundfrom a receiver 16 within the case to a further air tube which extendsinto the ear of the hard-of-hearing person.

Those skilled in the art will appreciate that the air tube 14-advantageously may be formed of a stiff plastic material so that it maybe shaped to fit the ear and rest comfortably thereon. The air tube 14advantageously is embedded within the end piece 18, and is in soundcommunication with the receiver 16 through the aperture 24 in the nubbinprovided in end piece 18, and through the sealing ring 22 positionedbetween the nubbin and the receiver 16. Advantageously, the end piece 18may be secured to the hearing aid case 12 by means of any suitablefastener, such as the threaded screw fastener 24 which is positionedwithin a suitable threaded opening 26 in the hearing aid case.

In addition to the receiver 16, the hearing aid within the case 12comprises an amplifier and control portion 28 which is positionedimmediately adjacent the receiver portion 16. While the amplifier andcontrol portion 28 is shown in FIGURE 1 as having a cover 30 thereover,it will be appreciated that the amplifier and control portion 28 maycomprise any suitable transistorized amplifier and volume controlassembly, the volume control being adjustable externally by means ofvolume control knob 32.

A microphone 84 is positioned adjacent the amplifier and control portion28, and a combined On-Off switch and battery holder 36 is positionedadjacent the microphone. Advantageously, the combined On-Ofi switch andbattery holder 36 is pivotally attached to the hearing aid case by meansof the pivot member 38 so that the switch and battery holder 36 may beactuated to turn the hearing aid On or Off, or further actuated to bewithdrawn from the case for replacement or checking of the battery. Theswitch and battery holder 36 is provided with the suitable centralaperture 40 adapted to receive a battery therein and a pair of contacts42 and 44 are provided for engaging the battery terminals in a selectivemanner to control the energized condition of the hearing aid.

While the details of the hearing aid shown in FIGURE 1 are described forpurposes of illustrating one specific preferred embodiment of theinvention, manifestly, the invention is not limited to the hearing aidof FIGURE 1 and may be used with equally advantageous results in otherhearing aids as well as other compact electrical structures employingtransducers.

In accordance with a salient feature of this invention, the transducersof the hearing aid are suspended within the case in a unique and highlyadvantageous manner. The novel suspension means differs from thevisco-elastic isolators and suspension means of the prior art andovercomes the difiiculties associated therewith, as described in detailhereinabove.

One specific illustrative embodiment of transducer suspension means inaccordance with the invention is shown in FIGURES 1, 2, 3, and 4, of thedrawing. Advantageously, this illustrative embodiment takes the form ofa fiat, metallic spring which preferably comprises a plurality ofsinuous beams and which further comprises an isolator secured to thegeometric center of the fiat, metallic spring for supporting thetransducer in non-contacting relation with the spring and with the Wallsof the transducer case.

The nature of the properties required for a transducer suspension memberof the type contemplated by the present invention are as follows. Firstof all, the fundamental frequency of oscillation of the suspensionmember in combination with the transducer must be well below the lowestfrequency being amplified by the electrical device. For example, in thecase of a hearing aid in which the lowest frequency being amplified isapproximately 400 cycles, the transducer suspension member incombination with the transducer should have a natural period ofoscillation of no greater than cycles per second. Secondly, thoseskilled in the art will appreciate that a transducer, such as themicrophone, is much less sensitive to vibration at a plane parallel tothe microphone diaphragm than in a plane perpendicular to the diaphragm.As a result, the transducer suspension member advantageously is madevery stiff in a horizontal plane but very compliant in the verticalplane. This requirement is admirably met by the present invention sincethe fiat, sinuous, metallic spring has much greater stiffness in theplane in which vibration isolation is not required.

One practical result of this unique arrangement is the use of smallercavities for the transducers. Thus, a microphone in the hearing aid,when suspended by the invention, may be placed in a small cavity withmuch less concern about the problem of rapid head motion than is thecase with present day transducer suspension members.

A still further advantage of the fiat, metallic transducer suspensionmember of the present invention is the fact that its properties can beheld to very close tolerances. Thus, metallic materials, such asstainless steel, do not deteriorate with time as is the case of spongerubber or other visco-elastic materials, and therefore the suspensionmember can be maintained to a desired degree of performance.

In the specific illustrative embodiments of transducer suspensions shownin FIGURES 1 to 4, the transducer suspension member 56 is a fiat,metallic spring which is sinuous in shape and which is provided at itsends with the terminal pieces 52 and 54, respectively. The sinuous shapeof the transducer suspension member 50 is highly advantageous to givethe suspension member a greater effective length in a relatively smallarea. Those skilled in the art will appreciate that this action of thesuspension member 50 may be viewed as the action of several F springs intandem. Effectively many beam means are provided in series to permitefficient isolation of the transducer from case vibration.

As shown in FIGURES l, 2, and 3 of the drawing, the terminals 52 and 54of the transducer suspension member 52 are positioned on the shoulders56 and 58, respectively, of the transducer cavity provided in thehearing aid case. The transducer suspension member 50 can be held inposition by any suitable means and the cover of the case is positionedthereover to maintain the suspension member securely in its desiredposition.

FIGURE 2 shows the microphone 34 of the hearing aid as suspended fromthe transducer suspension member 59 by means of the isolator orseparator element 58. Similarly, FIGURE 3 shows a receiver 16 of thehearing aid as suspended from the transducer suspension member 559 bymeans of the isolator element 58. in accordance wit a feature of thisinvention, the isolator element 58 is mounted at geometric center of thetransducer suspension element 58 so that the transducer is innon-contacting relationship with the suspension member 50 and further innon-contacting relationship with the walls of the transducer cavity inthe case 12 Due to the low internal damping of the fiat metallictransducer suspension members 50, there is a possibility that such amember may be excited into substantial resonance at higher frequencies.In accordance with a further embodiment of this invention, suchoscillation or vibration at higher frequency modes may be suppressed byproviding sufficient damping for the metallic spring suspension member.Thus, as illustrated in FIGURE 5 of the drawing, a transducer such asthe microphone 34 may be suspended by the isolator from a transducersuspension member 62 of damped construction. As shown in FIGURE 5, thetransducer suspension member 62 advantageously comprises a layer ofvisco-elastic material as which is sandwiched between a flat, metallicspring member 55 and a very thin layer of stiff constraining material,such as a sheet of aluminum foil d6. Those skilled in the art willreadily appreciate that the damping action provided by the dampedsuspension member arrangement of FIGURE 5 will serve to inhibit orsuppress any tendency of the transducer suspension member to vibrate atigher frequencies.

A still further embodiment of the invention which is adapted to providegreater isolation at frequencies above the natural period of the springis shown in FIGURES 6 and 7 of the drawing. As illustrated in thesefigures, this embodiment comprises the transducer suspension element 50dscribed hereinabove, and an isolator or spacer 58 secured to thesuspension member, which in turn supports a transducer, such as amicrophone 34. In addition to these elements, which correspond to theconstuctions described in respect to FIGURES 1 through 4, thisembodiment further comprises an additional spacer or isolator 70 securedto the opposite side of the transducer suspension member fit forsupporting an additional spring and mass arrangement to provide dampeddynamic vibration absorption.

The equivalent circuit for the damped dynamic vibration absorber isshown in FIGURE 6 of the drawing wherein the microphone 34 is shown assuspended by a spring element K. Spring element K corresponds to thespring suspension provided by the transducer suspension member 50.Suspended from the microphone 34 is shown an additional spring k and anadditional damping means 1', shown in parallel and supporting anadditional mass m. The additional spring damping means and mass areprovided in one practical form of such a suspension by a thin, rubberdisc '72 mounted on the isolator '79. The additional mass m is providedby the actual ettective mass of the rubber disc '72 and the additionalSpring 11' is provided by the compliance of the rubber disc 72 when itvibrates in the umbrella mode.

In another embodiment of the damped dynamic vibration absorberarrangement, the total mass would be the actual effective mass of therubber disc 72 in addition to the mass of an annular lead ring 74positioned around the rubber disc 72. Thus, the mass element 212 couldbe provided by a rubber disc alone or by the combination of a rubberdisc and a metal ring thei'earound.

One typical value for such mass would be approximately /5 of the mass ofthe transducer. Thus, in a microphone having a mass of 2 grams, forexample, the mass of the damped dynamic vibration absorber element wouldbe approximately of a gram.

While many other embodiments of transducer suspension members will besuggested in accordance with the teachings of the present invention, theabove specifically described embodiments are merely illustrative ofseveral practical forms of the invention to comply with therequirernents of the patent statutes.

In addition to overcoming many of the problems of prior artvisco-elastic transducer suspension members, the transducer suspensionmember of the invention also may be used in providing highly eificientacoustic isolation between a receiver and a microphone in a hearing aidcase. Thus, those skilled in the art know that a certain amount of theacoustic output from the receiver normally is incident upon themicrophone within the same hearing aid case. Some of this output comesfrom the leaks around joints, which usually are in the places where thereceiver is connected to the nubbin.

The output then travels to the microphone through the case cavity. Someacoustic output may be radiated into the case cavity from the vibrationon the walls of the receiver itself. if a receiver in a a hearing aid isviewed as a miniature loud speaker, it can be appreciated how soundpressure developed in the receiver can vibrate the walls of the receivercase. This acoustic output adds to the acoustic output leaks and alsoreaches the microphone.

In accordance with a feature of this invention, such acoustic feedbackmay be reduced for transducers suspended by flat, metallic springsuspension members Si? by placing the entire receiver in a scaled cavitywith stiil walls, or by molding a simple acoustic attenuator into thehearing aid case. In the latter, such an attenuator may take the form ofa quarter-wave acoustic trap for frequencies at which the receiverdevelops its peak output.

Another highly advantageous embodiment of the invention is illustratedin FIGURES 9 and 10 of the draw ing. Those skilled in the art willreadily appreciate that the vibration of a transducer during its normaloperation requently results in breakage of the relatively thintransducer electrical leads. This serious problem is overcome inaccordance with a feature of the invention by the utilization of themetallic elements of the damped vibration isolator of FIGURE 5 as twoterminal electrical conductors. Thus, as shown in FIGURES 9 and 10, thetransducer 34 normally is provided with the electrical conductor leadsand 84. One lead 84 is electrically connected to the metallic springmember 50 of the suspension member 62 and the other lead 80 iselectrically connected to the sheet of metallic foil 66 positioned on ne layer of visco-elastic material 64 opposite the spring mem ber 50.

Preferably, the point of connection for each of the leads is at thegeometric center of the suspension system. Since there is no relativemotion between the transducer 34- and the geometric center of thesuspension system the leads an and are not caused to vibrate and thebreakage problem is substantially reduced. The electrical output fromthe transducer 3 is obtained from the two conductors :52 and 3:?attached to the extrem ends of metallic elements 66 and 5% respectively.As the extreme ends of the spring Ell are supported by the case wall,there is no relative motion on these points. Consequently, relativelyheavy electrical leads 82 and 86 may be alrlxed in a suitable manner atthese points to carry the electrical output from the transducer to theelectrical amplifying system of the hearing aid or other compact elctrical device.

While there has been shown and described a particular embodiment of thisinvention, it will be obvious to those skilled in the art that variouschanges and modifications may be made therein without departing from theinven tion and, therefore, it is intended in the appended claims tocover all such changes and modifications as fall within the true spiritand scope of the invention.

What I claim as my invention is:

1. The improvement of transducer mounting means for supporting atransducer within a hearing aid case comprising a plurality of sinuous,series connected beam secured to the walls of a transducer cavity withinthe case, a transducer, attachment means secured to said beams andsupporting said transducer in non-contacting relation with said beamsWithin said transducer cavity, said transducer also being supported bysaid attachment means in noncontacting relation with the walls of saidtransducer cavity.

2. The improvement of transducer mounting means for supporting atransducer within a cavity in a hearing aid case comprising flat,metallic beam means, said beam means comprising a plurality of seriesconnected beams having a pair of opposed terminal ends secured to thewalls of said case, a transducer, attachment means secured to said beammeans and to said transducer for supporting the latter in non-contactingrelation with said beam means within said transducer cavity.

3. The improvement of transducer mounting means for supporting atransducer within a hearing aid case comprising fiat, resilient beammeans secured to the Walls of a transducer cavity within the case, atransducer, separator means geometrically centered on said beam meansand supporting said transducer in non-contacting relation with the wallsof said transducer cavity, and damping means secured to said beam meansfor damping vibrations at higher frequencies to prevent said beam meansfrom becoming excited into resonance at such higher frequencies.

4. The improvement of transducer mounting means in accordance with claim3 wherein said damping means comprises a layer of a visco-elasticmaterial adjacent said beam means and a sheet of stiff constrainingmaterial positioned on the visco-elastic layer.

5. The improvement of transducer mounting means in accordance with claim4 wherein said sheet of stiff constraining material comprises a sheet ofaluminum foil.

6. The improvement of transducer mounting means for supporting atransducer Within a hearing aid case comprising flat, metallic beammeans secured to the walls of a transducer cavity within the case, atransducer, first isolator means located at the geometric center of oneside of said beam means and supporting said transducer in non-contactingrelation with the walls of said transducer cavity, second isolator meanslocated at the geometric center of the other side of said beam means,and clamped dynamic vibration absorber means supported by said secondisolator means.

7. The improvement of transducer mounting means in accordance with claim6, wherein said damped dynamic vibration absorber means comprises a thinresilient disc, the mass of said disc serving as the mass of thevibration absorber means and the compliance of said disc serving as thespring of said vibration absorber means.

8. The improvement of transducer mounting means in accordance with claim'7 further comprising an additional mass for said vibration absorbermeans formed of an annular lead ring mounted around said resilient disc.

9. The improvement of transducer mounting means for supporting atransducer within a case containing electrical circuitry comprisingfiat, resilient, metallic beam means secured to the walls of atransducer cavity within the case, a transducer, separator means securedto said beam means and supporting said transducer in non-contactingrelation with the walls of said transducer cavity, damping means securedto said beam mean for damping vibrations at higher frequencies, saiddamping means comprising a layer of visco-elastic material positioned onsaid metallic beam means and a sheet of thin metallic foil positioned onsaid visco-elastic layer, and means connccting one electrical lead ofsaid transducer to the metallic beam means and the other electrical leadof said transducer tothe sheet of metallic foil whereby the latterserves as two conductive terminals for connecting said transducer to theremainder of the electrical circuit.

10. The improvement of transducer mounting means in accordance Withclaim 9 wherein said transducer electrical leads are connected to thegeometrical centers of said beam means and metallic foil sheet tominimize vibration of said leads and thereby reduce lead breakageproblems.

References Cited in the file of this patent UNITED STATES PATENTS2,260,727 Sears et al. Oct. 28, 1941 FOREIGN PATENTS 104,229 Sweden Apr.14, 1942

1. THE IMPROVEMENT OF TRANSDUCER MOUNTING MEANS FOR SUPPORTING ATRANSDUCER WITHIN A HERAING AID CASE COMPRISING A PLURALITY OOF SINOUSSERIES CONNECTED BEAMS SECURED TO THE WALLS OF A TRANSDUCER CAVITYWITHIN THE CASE,